This invention relates generally to pulsed laser, high power optical amplifier system and more particularly to pulsed semiconductor laser high power fiber amplifier systems for material processing such as in the case of thermally treating polymeric, ceramic and metal surfaces, including but not limited to, surface texturing, heat treatment, surface engraving, surface ablation, cutting, grooving, bump forming, coating, sealing, soldering, surface diffusion and surface conversion to a compound. A particular example is shown for surface texturing of disk surfaces, such as for texturing of magnetic disk substrate surfaces upon which is formed a thin magnetic film comprising a magnetic hard disk employed in digital magnetic recording systems.
Material processing has been used with Nd:YAG lasers and gas lasers, e.g. CO2 lasers, to process treat polymeric, ceramic and metal surfaces, including but not limited to surface texturing, heat treatment, surface engraving, micro-machining, surface ablation, cutting, grooving, bump forming, coating, sealing, surface diffusion and surface conversion to a compound. One such process example is surface texturing for magnetic disk media used in magnetic disk systems. In present day magnetic disk systems, particularly magnetic rigid disks used for recording data, the surfaces of the disks are textured, i.e., provided with a plurality of microscopic grooves or bumps across or in portions of the disk surfaces to improve the properties of the disk both mechanically and magnetically. Surface texturing mechanically removes the Johansson block effect which is the tendency for flying magnetic, air bearing slider in a magnetic head, employed in magnetic disk drives, to adhere to the flat substrate magnetic surface of a magnetic medium. This is referred to as stiction wherein the air bearing slider has been stationary on the magnetic recording surface for a period of time, the slider resists any transitional movement and is prone to adhere to the magnetic surface. Texturing removes, if not eliminates, such slider adhesion. Also, mechanically, the grooves provide a place or reservoir for loose microscopic materials developed over time to lodge out of the way of the flying head. Magnetically, surface texturing enhances the magnetic surface properties by reducing the magnetic radial component while intensifying the circumferential magnetic component. After surface texturing, a thin magnetic film is formed on the textured disk surfaces. Intermediate layers may be utilized prior to magnetic film formation to improve the adherence and magnetic properties of the film.
In the past, the texturing processing has been carried out using a fixed or free abrasive medium, such as a tape, applied to the surface of the disk substrate. See, for example, U.S. Pat. Nos. 4,964,242; 5,088,240; and 5,099,615 assigned to Exclusive Design Company, Inc. of San Mateo, Calif.
Texturing also has been accomplished employing a texturing pad in combination with a particle slurry as taught in U.S. Pat. No. 5,167,096. Also, chemical etching has been employed for texturing as disclosed in U.S. Pat. No. 5,576,918. Recently, the use of lasers have been applied for texturing substrate surfaces for magnetic disks. Examples of such laser texturing systems are disclosed in U.S. Pat. Nos. 5,062,021; 5,567,484; 5,550,696; and 5,528,922 for overcoming stiction between the magnetic disk medium and the magnetic head slider when the slider starts and stops relative to the magnetic disk surface or in texturing an outer annular surface of the disk for use in Contact Start/Stop (CSS) cycling of the magnetic head. In most of these cases, a CO2 gas laser or Q-switched Nd:YAG (Nd:YLF or Nd:YVO4) laser having, for example, a wavelength around 1060 nm with a repetitive pulse rate of 70 kHz to 100 kHz and pulse width of about 60 or 70 xcexcsec have been employed. In Q-switched Nd:YAG laser systems, the noise specification is around 2% rms. These laser systems are integrated into a laser texturing head where the output beam is split using waveplates or cubic beam splitters so that the split beam is routed to opposite surfaces of the disk to be textured.
However, these systems have no ability for directly providing pulse stability, pulse-to-pulse repeatability as well as selected pulse width and shape configuration. As an example, the pulse width and shape in Q-switched Nd:YAG laser systems cannot be changed on-the-fly in pulse width and pulse shape with time such as double stepped amplitudes or ramp-up and ramp-down variations.
It is a primary object of this invention to provide a pulsed semiconductor laser high power fiber amplifier system for material processing.
It is another object of this invention to provide a modulated diode laser and fiber amplifier system capable of providing 10 mW of pulse input power and produce output powers in hundreds of watts to several kilowatts for material processing applications with very low pulse to pulse energy fluctuations.
Also in laser texturing as a exemplary example of material processing, what is desired is a laser texturing head that is lighter in weight and smaller in size that is not so bulky, compared to the task at hand, and are capable of the same and even higher power delivery for texturing with pulse stability and pulse-to-pulse repeatability, which is another object of this invention.
It is a another object of this invention is to provide a high power laser optical amplifier system of comparatively small compact size for texturing the surfaces of disk substrates employed in magnetic recording systems.
It is a further object of this invention to provide a high power laser optical amplifier system that has sufficiently high power to process treat polymeric, ceramic and metal surfaces, including but not limited to, surface texturing, heat treatment, surface engraving, micro-machining, surface ablation, cutting, grooving, bump forming, coating, sealing, soldering, surface diffusion and surface conversion to a compound.
According to this invention, a pulsed semiconductor laser high power fiber amplifier system for material processing comprises at least one fiber amplifier capable of rejection of propagating ASE buildup in and between the amplifier stages as well as elimination of SBS noise providing output powers in the range of about 10 xcexcJ to about 100 xcexcJ or more resulting in low pulse to pulse energy fluctuations. The system is driven with a time varying drive signal from a modulated semiconductor laser signal source to produce an optical output allowing modification of the material while controlling its thermal sensitivity by varying pulse shapes or pulse widths supplied at a desire repetition rate via modulation of a semiconductor laser signal source to the system to precisely control the applied power application of the beam relative to the thermal sensitivity of the material to be processed.
A pulsed semiconductor fiber laser high power amplifier system of this invention further comprises a semiconductor laser pumped, multi-stage fiber amplifier with means for rejecting amplified stimulated emission (ASE) buildup in and between the amplifier stages which is a problem in achieving higher power outputs in fiber amplifier systems. ASE rejection means utilized in this invention comprises the employment of one or more of an optical circulator, a narrow band WDM, or a dB coupler with peak injection signal gratings at coupler terminal ports. The system may be operated cw or pulsed. The ASE inhibited fiber amplifying system provides a laser source and fiber amplifier system that is capable of providing an amplified modulated pulse output having high long term pulse stability, e.g., below 1% rms, with ability to provide pulse width and pulse contour selectability, not readily capable with YAG systems, and providing a pulse output up to 100 xcexcJ for delivery to an applied application such as in the exemplary application herein of disk texturing. The system with ASE rejection also has high utility for signal modulation and amplification in optical communication systems.
The basic components of the pulsed semiconductor laser high power fiber amplifier system is a laser diode source or diode laser array source, coupled to means to isolate the laser source from feedback noise, which is coupled to a first stage single mode fiber amplifier followed by a second stage double clad fiber amplifier.
Also, the pulsed semiconductor laser high power fiber amplifier system of this invention eliminates problems with SBS by providing a semiconductor laser source having multiple wavelengths to increase the SBS threshold by the number of multimodes present so that the stages of amplification are relatively free of SBS. The multimode output of the laser source may be coupled to a multimode fiber followed by a cladding pump or double clad fiber amplifier. The semiconductor laser source may be operated in multimode by having attached to it a pigtail fiber with a fiber Bragg grating designed to provide optical feedback to the laser that drives the laser into multimode operation.
The pulsed semiconductor laser high power fiber amplifier system of this invention is capable of providing pulse peak powers of about 0.1 kW to about 10 kW with a modulated semiconductor laser as initial input power of about 10 mW with pulse widths of about 10 nsec to about 100 nsec and capable of being modulated at repetition rates between 10 kHz and 1 MHz providing an output power from the system in the range of about 10 xcexcJ to about 100 xcexcJ.
The pulsed semiconductor laser high power fiber amplifier system of this invention is applicable for many applications such as fine micro-machining or surface texturing. In surface texturing of magnetic disk substrates, the system of this invention replaces texturing techniques such as chemical etching employed in the texturing process as set forth in U.S. Pat. No. 5,162,073 or YAG laser systems employed in the texturing process as set forth in U.S. Pat. Nos. 5,062,021; 5,567,484; 5,550,696; and 5,528,922. Also, this invention has excellent utility for engraving surfaces such as ceramic and metal surfaces used in gravure type or ablative off-set printing systems as disclosed in U.S. Pat. Nos. 5,236,763 and 5,385,092, as well as other applications that can successfully employ high amplification of laser diode signal with high rejection of ASE, such as in optical isolators, optical communications and LIDAR.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.